The present application is based on and claims priority from Japanese Patent Applications 2000-64852, filed Mar. 9, 2000 and 2000-127386, Apr. 27, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a bearing device for a vehicle rotary machine, such as an AC generator that has a pair of bearings.
2. Description of the Related Art
A vehicle rotary device having a bearing device such as an AC generator is sometimes installed at a position in a vehicle""s engine compartment where mud water may splash it.
If a bearing of the bearing device is covered with mad water, the balls of the bearing may rust or the grease of the bearing may deteriorate. As a result, the bearing device generates noise and/or vibration.
JP-A-11-82526 discloses a bearing that has a pair of sealing members covering opposite sides of the bearing to seal a space in which a plurality of rolling members are accommodated. The pair of sealing members has elastic lips in contact with the outer periphery of the inner ring and is fixed to the opposite sides of the outer ring thereof.
However, because such bearings are used under comparatively a high temperature condition, the lips of the sealing member may deteriorate. As a result, the sealing member cannot seal the bearing space completely. If the lips of all the bearings are made of a heat resistant rubber, the bearings become too expensive.
A main object of the invention is to provide an inexpensive bearing device that is resistant to heavy environmental conditions.
According to a feature of the invention, a bearing device includes a pair of bearings, one of which is exposed to a higher temperature condition than the other. Each of the bearings has an outer ring, an inner ring, a plurality of rolling members disposed in a space between the outer ring and the inner ring and a pair of sealing members fixed to the outer ring to cover the space. Each of the sealing members has an elastic lip in contact with outer surfaces of a corresponding one of the inner rings, and the lip of the bearing exposed to a higher temperature condition is made of a more heat-resistant material than the lip of the other bearing, such as fluoro rubber that is more heat-resistant than any one of nitrile rubber and acrylic rubber.
Therefore, an additional cost for providing a heat-resistant bearing device is very small.
The outer ring of the bearing exposed to a higher temperature condition is preferably made of high carbon-chromium bearing steel that includes silicon at a ratio between 0.5% and 1.2%, which is higher than the material of the outer ring of the other bearing, which usually includes silicon at a ratio between 0.15% and 0.35%.
The outer ring of the bearing exposed to a higher temperature condition may be made of a high carbon-chromium bearing-steel that includes retained austenite of less than 10%.
It is also preferable that the bearing exposed to a higher temperature condition is made of higher anticorrosive material than the other bearing, such as stainless steel or ceramic.